[PATCH v3 4/7] rtc: spacemit: support the SpacemiT P1 RTC

[Alex Elder <elder@riscstar.com>]

Add support for the RTC found in the SpacemiT P1 PMIC.  Initially
only setting and reading the time are supported.

The PMIC is implemented as a multi-function device.  This RTC is
probed based on this driver being named in a MFD cell in the simple
MFD I2C driver.

Signed-off-by: Alex Elder <elder@riscstar.com>
---
v3: - Added this driver to the series, in response to Lee Jones saying
      more than one MFD sub-device was required to be acceptable

 drivers/rtc/Kconfig  |  10 ++++
 drivers/rtc/Makefile |   1 +
 drivers/rtc/rtc-p1.c | 137 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 148 insertions(+)
 create mode 100644 drivers/rtc/rtc-p1.c

diff --git a/drivers/rtc/Kconfig b/drivers/rtc/Kconfig
index 9aec922613cec..27cff02ba4e66 100644
--- a/drivers/rtc/Kconfig
+++ b/drivers/rtc/Kconfig
@@ -406,6 +406,16 @@ config RTC_DRV_MAX77686
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-max77686.
 
+config RTC_DRV_P1
+	tristate "SpacemiT P1 RTC"
+	depends on ARCH_SPACEMIT || COMPILE_TEST
+	select MFD_SPACEMIT_P1
+	default ARCH_SPACEMIT
+	help
+	  Enable support for the RTC function in the SpacemiT P1 PMIC.
+	  This driver can also be built as a module, which will be called
+	  "spacemit-p1-rtc".
+
 config RTC_DRV_NCT3018Y
 	tristate "Nuvoton NCT3018Y"
 	depends on OF
diff --git a/drivers/rtc/Makefile b/drivers/rtc/Makefile
index 4619aa2ac4697..f8588426e2ba4 100644
--- a/drivers/rtc/Makefile
+++ b/drivers/rtc/Makefile
@@ -171,6 +171,7 @@ obj-$(CONFIG_RTC_DRV_SD2405AL)	+= rtc-sd2405al.o
 obj-$(CONFIG_RTC_DRV_SD3078)	+= rtc-sd3078.o
 obj-$(CONFIG_RTC_DRV_SH)	+= rtc-sh.o
 obj-$(CONFIG_RTC_DRV_SNVS)	+= rtc-snvs.o
+obj-$(CONFIG_RTC_DRV_P1)	+= rtc-p1.o
 obj-$(CONFIG_RTC_DRV_SPEAR)	+= rtc-spear.o
 obj-$(CONFIG_RTC_DRV_STARFIRE)	+= rtc-starfire.o
 obj-$(CONFIG_RTC_DRV_STK17TA8)	+= rtc-stk17ta8.o
diff --git a/drivers/rtc/rtc-p1.c b/drivers/rtc/rtc-p1.c
new file mode 100644
index 0000000000000..e0d2c0c822142
--- /dev/null
+++ b/drivers/rtc/rtc-p1.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for the RTC found in the SpacemiT P1 PMIC
+ *
+ * Copyright (C) 2025 by RISCstar Solutions Corporation.  All rights reserved.
+ */
+
+#include <linux/bits.h>
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+
+#define MOD_NAME	"spacemit-p1-rtc"
+
+/* Offset to byte containing the given time unit */
+enum time_unit {
+	tu_second = 0,		/* 0-59 */
+	tu_minute,		/* 0-59 */
+	tu_hour,		/* 0-59 */
+	tu_day,			/* 0-30 (struct tm uses 1-31) */
+	tu_month,		/* 0-11 */
+	tu_year,		/* Years since 2000 (struct tm uses 1900) */
+	tu_count,		/* Last; not a time unit */
+};
+
+/* Consecutive bytes contain seconds, minutes, etc. */
+#define RTC_COUNT_BASE		0x0d
+
+#define RTC_CTRL		0x1d
+#define RTC_EN		BIT(2)
+
+struct p1_rtc {
+	struct regmap *regmap;
+	struct rtc_device *rtc;
+};
+
+static int p1_rtc_read_time(struct device *dev, struct rtc_time *t)
+{
+	struct p1_rtc *p1 = dev_get_drvdata(dev);
+	u8 time[tu_count];
+	int ret;
+
+	ret = regmap_bulk_read(p1->regmap, RTC_COUNT_BASE, &time, sizeof(time));
+	if (ret)
+		return ret;
+
+	t->tm_sec = time[tu_second] & GENMASK(5, 0);
+	t->tm_min = time[tu_minute] & GENMASK(5, 0);
+	t->tm_hour = time[tu_hour] & GENMASK(4, 0);
+	t->tm_mday = (time[tu_day] & GENMASK(4, 0)) + 1;
+	t->tm_mon = time[tu_month] & GENMASK(3, 0);
+	t->tm_year = (time[tu_year] & GENMASK(5, 0)) + 100;
+	/* tm_wday, tm_yday, and tm_isdst aren't used */
+
+	return 0;
+}
+
+static int p1_rtc_set_time(struct device *dev, struct rtc_time *t)
+{
+	struct p1_rtc *p1 = dev_get_drvdata(dev);
+	u8 time[tu_count];
+	int ret;
+
+	time[tu_second] = t->tm_sec;
+	time[tu_minute] = t->tm_min;
+	time[tu_hour] = t->tm_hour;
+	time[tu_day] = t->tm_mday - 1;
+	time[tu_month] = t->tm_mon;
+	time[tu_year] = t->tm_year - 100;
+
+	/* Disable the RTC to update; re-enable again when done */
+	ret = regmap_update_bits(p1->regmap, RTC_CTRL, RTC_EN, 0);
+	if (ret)
+		return ret;
+
+	ret = regmap_bulk_write(p1->regmap, RTC_COUNT_BASE, time, sizeof(time));
+
+	(void)regmap_update_bits(p1->regmap, RTC_CTRL, RTC_EN, RTC_EN);
+
+	return ret;
+}
+
+static const struct rtc_class_ops p1_rtc_class_ops = {
+	.read_time = p1_rtc_read_time,
+	.set_time = p1_rtc_set_time,
+};
+
+static int p1_rtc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct rtc_device *rtc;
+	struct p1_rtc *p1;
+	int ret;
+
+	p1 = devm_kzalloc(dev, sizeof(*p1), GFP_KERNEL);
+	if (!p1)
+		return -ENOMEM;
+	dev_set_drvdata(dev, p1);
+
+	p1->regmap = dev_get_regmap(dev->parent, NULL);
+	if (!p1->regmap)
+		return dev_err_probe(dev, -ENODEV, "failed to get regmap\n");
+
+	rtc = devm_rtc_allocate_device(dev);
+	if (IS_ERR(rtc))
+		return dev_err_probe(dev, PTR_ERR(rtc),
+				     "error allocating device\n");
+	p1->rtc = rtc;
+
+	rtc->ops = &p1_rtc_class_ops;
+	rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	rtc->range_max = RTC_TIMESTAMP_END_2063;
+
+	clear_bit(RTC_FEATURE_ALARM, rtc->features);
+	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->features);
+
+	ret = devm_rtc_register_device(rtc);
+	if (ret)
+		return dev_err_probe(dev, ret, "error registering RTC\n");
+
+	return 0;
+}
+
+static struct platform_driver p1_rtc_driver = {
+	.probe = p1_rtc_probe,
+	.driver = {
+		.name = MOD_NAME,
+	},
+};
+
+module_platform_driver(p1_rtc_driver);
+
+MODULE_DESCRIPTION("SpacemiT P1 RTC driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:" MOD_NAME);
-- 
2.45.2